1. Field of the Invention
The present invention relates to a power source control apparatus and method for a computer system having a rechargeable battery in addition to an AC power source as a system power source.
2. Description of the Related Art
In conventional compact (e.g., lap-top type) computers, a method of driving the computer by a rechargeable battery power source mounted in the computer is known. In a computer adopting this method, when an AC power source is used as a system power source, electric power excluding an electric power amount to be supplied to the system is used for charging a battery.
The computer mounts a display (e.g., a plasma display) for displaying data. Some computers, which can perform a display in a high brightness display mode (shown by reference numeral 1 in FIG. 1), are available. The high brightness display mode requires a large electric power amount although the display performance can be improved as compared to a normal brightness display mode (shown by reference numeral 3 in FIG. 1).
For this reason, when a display operation in the high brightness display mode is executed, the electric power amount that can be used for charging the battery is often considerably decreased. In practice, when data is displayed on the display in the high brightness display mode, if the display rate (a percentage of number of pixels which are turned on with respect to total number of pixels constituting a display screen) of data on the display screen is increased, extra electric power is consumed for the display operation, and electric power for charging the battery can no longer be obtained. Thus, it becomes impossible to charge the battery.
In another method, an electric power amount excluding an electric power amount used for the display operation of the total electric power amount used by the system power source is automatically used for charging the battery. However, when the display operates in the high brightness display mode, the electric power amount that can be used for charging the battery is considerably decreased, and it becomes practically impossible to charge the battery.
In this case, although an effective charge operation cannot be made in practice, the system automatically executes the charge operation of the battery, and informs a message indicating the execution of the charge operation to a user. For this reason, the charging time of the battery is apparently prolonged, and an LED lamp indicating a low battery does not turn from red (low battery) to green (full charge). Therefore, a user may erroneously recognize that the system is malfunctioning.
Furthermore, a long charging time is required in order to obtain the full charge, and hence, the battery is overheated. As a result, the system may be damaged. Note that a method for detecting the full charge is described in U. S. Ser. No. 07/578,613, for example.